In recent years, spin electronics devices utilizing the spin freedom of electrons have been actively researched and developed. Active research and development based on the tunnel magnetoresistance (TMR) effects have led to applications such as magnetic random access memories (MRAMs) and read heads in hard disk drives (HDDs). Further, spin transistors formed by combining semiconductor and magnetic material are drawing attention.
As a reconfigurable logic circuit developed based on today's semiconductor technologies, there is an integrated circuit called FPGA (Field Programmable Gate Array). An FPGA stores information in static random access memories (SRAMs) provided therein, and, based on the information stored in the memories, the FPGA can control logics and connections in the reconfigurable logic circuit. As logics can be changed by software, corrections can be made to circuits after the manufacture of hardware. In recent years, this technique has rapidly spread as the means to realize complicated integrated circuits in short periods of time at low costs.
A large number of switching box circuits are used in an FPGA. A switching box circuit is a circuit that stores a connected state of signal lines extending from four different directions, and determines inputs and outputs through the signal lines, and connections and disconnections among the signal lines. A circuit including such switching box circuits can realize any connected state by rewriting the memories.
In a switching box circuit, the output of a memory is connected to a pass transistor circuit. Each pass transistor circuit serves as a switch, and determines a connection and a disconnection between signal lines, based on the information stored in the memory.
Where a switching box circuit is manufactured by semiconductor CMOS technology, SRAMs are used as memories to store information. Therefore, the number of devices becomes large. Since such a switching box circuit uses a large number of SRAMs, the power consumption becomes large due to the leakage current even when any operation is not being performed. As a result, it becomes difficult to achieve high integration with such circuits.
As a large number of pass transistor circuits are used in each one switching box circuit, the circuit size becomes extremely large, and becomes one of the factors that hinder high integration.
Further, SRAMs are volatile memories that lose information once the power supply is cut off. Therefore, every time the power supply is switched on, information stored in an external memory needs to be written into those SRAMs. As a result, trouble and time need to be taken every time the power supply is switched on.
There is a need to prepare the external memory to store information when the power supply is cut off, and extra power and space are required for the external memory. This is one of the factors that hinder high integration and a decrease in power consumption in the entire system.